Verify the retained 0.6.0 workflows and release readiness

After the recovery work completes, verify released-to-new workflows across retained APIs,
packaging and imports, persistence and migration examples. Run `uv run poe ok`; selected
integration workflows and executed tutorials and docs; real GPU checks for the retained GPU
claims. Confirm the 0.6.0 docs and export inventory exclude BrainCollection while recording
the 0.6.1 deferral.

Acceptance: evidence recorded at the final revision, no unexplained contract gaps, release
docs consistent, and any remaining limitations explicitly approved.

## Rulings

> Verification follows development/release-verification.md. Includes CUDA execution on pika
> after a user-home checkout and uv install, MPS execution locally, one full slow run,
> docs-build, packaging smoke, persistence, export inventory and migration examples.

> 2026-09-12: the benchmarks harness deselection is void (benchmarks/ was deleted). The
> Procrustes orientation question is settled inside the alignment slice.

> Ruling 2026-09-12 on the changelog: changelog entries live in commit messages;
> docs/changelog.md is git-cliff output regenerated by `poe changelog` at release. Earlier
> slices' hand-written entries are overwritten then — this issue runs `poe changelog` and
> reconciles.

> Push-time item still outstanding from the #491 merge: decide whether #491 stacks on or
> supersedes #483. (#493, #494 and #495 are already closed with commit references.)

This issue does not authorize publishing or tagging.

Blocked by: #505

Read development/release-verification.md first, then run `uv run poe ok` and follow the selected integration, tutorial, GPU, persistence, migration, packaging, docs-build, and export checks listed in the issue. Run `poe changelog` and reconcile docs/changelog.md. Done means evidence is recorded at the final revision, contracts and release docs are consistent, and approved limitations and the 0.6.1 deferral are documented.

Written by the indexing model from the issue text.